Moving to -std=gnu11 (another case for requiring GCC >= 4.7)

[Paul Eggert]

Joseph Myers wrote:
> What do people think of moving glibc to build with -std=gnu11 (the default
> in GCC 5 and later) instead of -std=gnu99?

I'd be in favor.  For what it's worth, -std=gnu11 will be the default for 
'configure' scripts generated the next Autoconf, whenever that comes out.